156 UNITY AND DIVERSITY IN BIOCHEMISTRY 



2. Phosphodiesterases 



O Q 



II II 



R^— O— P— OR' + H.O ^ R^— O— P— OH + K'OH 



I I 



OH OH 



Likewise their specificity with respect to R^ and R^ is low. In this group 

 are such universally distributed enzymes as ribonuclease and desoxy- 

 ribonuclease. 



3. Pyrophosphatases 



OH OH OH OH 



0=P— O— P=0 + H2O -^ 0==P— OH + 0=P— OH 



II II 



OR OH OR OH 



The adenosinetriphosphatases (ATPases), which catalyse the hydrolysis 

 of ATP to ADP and phosphoric acid, fall in this category. 



4. Metaphosphatases 



(HPOg)™ + wHaO-^wHaPOi 



{e) Deaminases 

 They catalyse the hydrolysis of the C — N bond of amines 



\ \ 



— C— NH2 4- H2O -» — C— OH + NHa 

 / / 



(/) Deamidases 

 They catalyse hydrolysis of the amide bond. 



-C— NH2 + H2O -^ — COOH + NH3 



Examples are urease, asparaginase, and glutaminase. Glutaminase 

 catalyses the hydrolysis of glutamine into glutamic acid and ammonia and 

 asparaginase of asparagine into aspartic acid and ammonia. 



